Laser-induced forward transfer (LIFT) has demonstrated its ability for high resolution printing of a large set of materials in solid or liquid phase. The typical dimension of the LIFT-printed structures is of few micrometers. By downscaling the donor film thickness together with the pulse duration and the spot size of the laser, sub-micrometers metal droplets have also been printed. Recently, we have proposed the double pulse LIFT process (DP-LIFT) which relies on the use of two laser beams to transfer metal droplets in liquid phase from a solid donor thin film. First, a quasi-continuous wave laser irradiates the thin metal donor film to locally form a liquid film, then, a second short pulse laser irradiates this area to induce the formation of a liquid jet and the printing of a small droplet on the receiver substrate.
We used time-resolved shadowgraphy to investigate the dynamics of high-velocity nanojets generated from solid copper films. These experiments show that this DP-LIFT approach induces the formation of very thin and stable liquid jets that expands over distances of few tens of micrometers for a large range of process conditions. We also demonstrated that the size of the melted metal pool plays an important role in the jet dynamics and allows controlling the size of the printed droplets. This process has been used to print 2D and 3D structures with micro and nano-meter sizes while avoiding the generation of any debris and these results demonstrates the high potential of DP-LIFT as a digital nano-printing process.
In this paper we show an experimental procedure for fabrication of metal nanoparticle arrays on metal substrates. The nanostructures are fabricated by laser processing of thin metal films. The films are deposited on the metal substrates by classical PLD technology. The as deposited films are then annealed by nanosecond pulses delivered from a THG Nd:YAG laser system (λ = 355 nm). At certain conditions, the laser treatment leads to a formation of discrete nanoparticle structure on the substrate surface. The optical properties of samples fabricated at different conditions and having different characteristics of the nanostructures are examined by optical spectroscopy measurement. Such analysis shows that the optical spectra of the obtained nanostructures are characterized by plasmon excitation. Finite difference time domain (FDTD) model is used for theoretical description of the near field optical properties of the fabricated nanoparticle arrays. The simulation demonstrates high efficiency of the fabricated structures in enhancement of the near field intensity. The great enhancement observed in the Raman spectra of Rhodamine 6G deposited on the fabricated samples makes such structures very appropriate for applications in Surface Enhanced Raman Spectroscopy (SERS). The produced systems can be also applied in plasmonic solar cells (PSC).
The development of organic electronic requires a non contact digital printing process. The European funded e-LIFT project investigated the possibility of using the Laser Induced Forward Transfer (LIFT) technique to address this field of applications. This process has been optimized for the deposition of functional organic and inorganic materials in liquid and solid phase, and a set of polymer dynamic release layer (DRL) has been developed to allow a safe transfer of a large range of thin films. Then, some specific applications related to the development of heterogeneous integration in organic electronics have been addressed. We demonstrated the ability of LIFT process to print thin film of organic semiconductor and to realize Organic Thin Film Transistors (OTFT) with mobilities as high as 4 10-2 cm2.V-1.s-1 and Ion/Ioff ratio of 2.8 105. Polymer Light Emitting Diodes (PLED) have been laser printed by transferring in a single step process a stack of thin films, leading to the fabrication of red, blue green PLEDs with luminance ranging from 145 cd.m-2 to 540 cd.m-2. Then, chemical sensors and biosensors have been fabricated by printing polymers and proteins on Surface Acoustic Wave (SAW) devices. The ability of LIFT to transfer several sensing elements on a same device with high resolution allows improving the selectivity of these sensors and biosensors. Gas sensors based on the deposition of semiconducting oxide (SnO2) and biosensors for the detection of herbicides relying on the printing of proteins have also been realized and their performances overcome those of commercial devices. At last, we successfully laser-printed thermoelectric materials and realized microgenerators for energy harvesting applications.
We investigate the non-linear absorption of 1.3 μm femtosecond laser pulses strongly focused inside silicon and fused
silica. Through transmission diagnostics, multiphoton initiated energy deposition is clearly observed inside these two
materials with nanojoules laser pulse energy when using 0.3 numerical aperture objective. For silicon, the non-linear
interaction is strongly dependent on the focusing depth due to the presence of spherical aberration contrarily to fused
silica. Below the surface, we find a difference of three orders of magnitude between the intensity thresholds for non-linear
absorption at 1.3 μm wavelength inside the two tested materials due to the difference of number of photons
required for non-linear absorption. By measuring the transmission of the ionizing pulses during multiple pulse
irradiation, irreversible modifications of the material are monitored inside fused silica in accordance with previous
studies at 800 nm. For similar laser energy deposition, the response of bulk silicon remains unchanged over more than
twenty thousands pulses suggesting no irreversible modifications are initiated.
Laser-matter interaction is a unique and simple approach to structure materials or locally modify their properties at the
micro and nanoscale level. Playing with the pulse duration and the laser wavelength, a broad range of materials and
applications can be addressed. Direct irradiation of surfaces with laser beam through a standard optical beam setup
allows an easy and fast structuring of these surfaces in the range of few micrometers. However, the irradiation of
materials through an array of dielectric nanospheres provides a unique opportunity to break the diffraction limit and to
realize structures in the range of hundred of nanometers. This simple, fast and low-cost near-field nanolithography
technique is presented and discussed, as well as its great potential.
The theoretical aspects of the near-field enhancement effects underneath the particles have been studied with a simple
model based on the Mie theory. A commercial FDTD software has also been used to study the influence of the substrate
and the surrounding media, on the energy profile of the photonic jet generated under the sphere. A specific study has
been dedicated to the influence of the dispersion of the sphere diameter on the morphology of the ablation craters. This
technique has been used for patterning bi-layer substrates. The process leads to the formation of a nanoporous membrane
which has been used to realize an array of gold nanodots on silicon. We have also associated the Laser-Induced Forward
Transfer (LIFT) process with the near-field nanolithography to print, in a single laser shot, an array of metallic
nanobumps.
3D laser microfabrication inside narrow band gap solids like semiconductors will require the use of long wavelength
intense pulses. We perform an experimental study of the multiphoton-avalanche absorption yields and thresholds with tightly focused femtosecond laser beams at wavelengths: 1.3μm and 2.2μm. For comparisons, we perform the experiments in two very different materials: silicon (semiconductor, ∼1.1 eV indirect bandgap) and fused silica (dielectric, ∼9 eV direct bandgap). For both materials, we find only moderate differences while the number of photons required to cross the band gap changes from 2 to 3 in silicon and from 10 to 16 in fused silica.
Laser near-field enhancements underneath transparent microspheres can be used to locally implement new functionalities in materials. Using this technique, we report micro- and nano-structuration on silicon (Si). The Langmuir-Blodgett (LB) technique is primarily used to realize monolayers of C18 functionalized silica (SiO2) microspheres on a large size area of the substrates. Afterwards, by irradiating the deposited monolayer with single shot UV nanosecond laser pulses in the ablation regime, we demonstrate the formation of dense arrays of craters in silicon substrate. In particular, we describe our works to obtain mono dispersed craters of sub micrometer size using LB technique and taking the fluence and sphere size as variable process parameters. Finite-difference time-domain (FDTD) simulations are presented to estimate the enhancement intensity factor and near-field distribution below the spheres in the experiments.
The processes involved in nanoparticle and nanostructure formation by laser are analyzed. Relative contributions of several mechanisms involved are compared. First, we consider the formation of "primary" particles and discuss the difference between femtosecond and nanosecond regimes. Then, "secondary" particle/aggregate formation is discussed. In particular, attention is focused on (i) direct cluster ejection from a target under rapid laser interaction; (ii) condensation/evaporation; (iii) fragmentation/aggregation processes during cluster diffusion; (iv) diffusion, aggregation, and/or coalescence. In addition, routes of control over particle size distribution are proposed. Possibility of formation of colloidal nanoparticles with very narrow size distribution is proven numerically. The role of such parameters as ablation yield, laser wavelength and laser fluence, and surface tension are examined. Finally, controlled nanoparticle self-assembly is discussed as a potential technique for future development of nanomaterials.
A comparative study of the ejection dynamic of organic materials by Laser-Induced Forward Transfer technique has
been performed using nanosecond and picosecond pulses for applications in plastic micro-electronics. The ejection of
organic materials has been carried out with various thicknesses and with and without a sacrificial metallic release layer
inserted between the substrate and the organic donor film. The advantage of this technique is to preserve organic layers
from being damaged by thermal and photochemical effects during the interaction. The dynamic of the process has been
investigated by shadowgraphic imaging during 1.5 μs after the laser irradiation, under atmospheric conditions. We have
determined the velocity of the transferred material and studied the influence of the metallic layer during the ejection
using a wide range of fluencies. The high directivity of the ejected material offers the possibilities of high spatial
resolution for the manufacture of micro-structures in non contact LIFT technique. The study of the influence of the
distance between the donor and acceptor substrates on the deposit functionality is discussed.
The unavoidable absorption of thin films used in antireflective coatings forms a permanent bottleneck in the
development of optics for high power laser applications. A valid alternative would be the micro-structuring of the optics
surface, realizing a diffraction grating which emulates the functioning of an Anti-Reflection thin film layer. Due to the
absence of film material, this diffractive structure would not contribute to the overall absorption of the optics. This paper
investigates the practical limits of this strategy, applied to zinc selenide as low absorption infrared substrate material.
We have prepared absorbing structures for photovoltaic cells with different nano-texturization, obtained by means of a
femtosecond laser, without the use of corrosive gas (i.e. under vacuum). To take in account the 3D structured front
surface, the emitter doping has been realized by using Plasma Immersion Ion Implantation (so-called PULSION). The
results show a photocurrent increase up to 60 % in the laser texturized zones.
Time- and space-resolved forward scattering detection was demonstrated as a suitable technique to characterize the dynamics of the ejected particles during dry laser cleaning. Silica particles with radii of 250 nanometers deposited on silicon substrates were irradiated by single nanosecond laser pulses with fluences above the particle removal threshold. The observation of different particle clouds propagating with different velocities was in support of the coexistence of at least two removal mechanisms. The ejection velocities were measured as a function of laser fluence in order to distinguish between the mechanisms involved in laser-assisted particle removal.
Femtosecond and nanosecond lasers are used to produce oxide nanoparticles by laser ablation of steel. The deposition of those particles on the surface strongly modifies its properties. The aim of this study is the understanding of the nanoparticle formation. The dynamics of the plume expansion and of the nanoparticle deposition processes are investigated by means of in-situ time resolved optical analysis. Scanning electron microscopy and atomic force microscopy are used to characterise the particle film morphology deposited on the surface. The influence of laser parameters such as pulse duration (ns, fs), wavelength (UV, visible, IR) and background gas pressure (10 mbar - 1 bar) on the processes of nanoparticle formation is studied. It is shown that a high density plasma favours the particle formation, and that the high temperature of the plume obtained with nanosecond JR irradiation impedes the nanoclusters nucleation and prevents an efficient nanoparticle formation.
The major bottleneck for the development of robust and cost-effective femtosecond amplification systems is the uncertainty concerning the damage threshold of Ti: Sapphire crystals. Up to now, Ti: Sapphire is the only material that supports the generation of temporally short pulses (few femtosecond) at high repetition rates, and overcoming this bottleneck will represent a major advance in laser performance for all the femtosecond community. Currently, when pumped at 532nm, the uncertainty on Ti:Sapphire damage threshold, is about a factor of ten. The empirically estimated threshold is 10J/cm2 but for safety reasons the femtosecond laser community (especially the companies producing the lasers) uses the conservative value of 1J/cm2. Such a low pumping fluency means low extraction efficiency during the amplification process and a great waste of pumping energy, the most expensive part of a Ti:Sapphire amplifier. In order to remove this bottleneck, we launch a complete analysis of all the factors that influence the damage threshold in Ti:Sapphire Crystals. Our program is to first measure the bulk threshold to define the upper threshold limit, and the influence of Ti ion concentration in the crystal garnet. Then, we will analyze all the surface effects that influence the value of the threshold. These effects depend on the polishing, on the cleaning process, as well as the type of anti-reflective coating. Only a complete understanding of all the mechanisms involved in threshold limitation will allow us to produce Ti:Sa crystals with the best performances. The study of the characteristics of the Ti:Sapphire damage threshold will not be complete and reliable without a complete characterization of the pump beams (temporal and spatial modulations), and this analysis will be done with nanosecond and picosecond pulses at 532nm. Finally, to complete the exploration of the the behavior of the titanium doped sapphire crystal, we will characterize the damage threshold with femtosecond pulses, at 800nm to reach the deterministic dielectric threshold and validate fundamentals models and simulation results. To our knowledges this is the first time that such a complete characterization is done for Ti:Sapphire laser crystals. We will present the first conclusions about the experiments as well as the methods we will employ in our systematic analysis.
KEYWORDS: Electrons, Gas lasers, Solid state lasers, Switches, Capacitors, Solid state electronics, Electrodes, Solid state physics, High power lasers, Dielectrics
The phototriggering has been proposed many years ago as a way to improve the reliability of excimer lasers. It is now a mature technique that is used in conjunction with the most recent solid-state devices to make an industrial high average power excimer laser. After a brief historical introduction we here analyze the main features and scientific aspects of this discharge technique and give very recent results.
First steps of development of an energetic (sub)nanosecond XeCl laser source are reported. For that purpose, a non- linear pulse shortening technique based on Stimulated Brillouin Scattering (SBS) is used for the temporal reshaping of an XeCl laser pump pulse. A compression factor of 10 has been demonstrated leading to the generation of a few nanosecond FWHM pulse duration pulses from a 65 mJ - 40 ns (FWHM) XeCl laser source. Further works are planned to improve the energy of the nanosecond Stokes pulse.
High contrast nanosecond pulse trains are produced by an oscillatorÑamplifier XeCl laser system incorporating polarizing optics. The device is simple and flexible allowing to deliver nanosecond pulse trains up to 17 mJ and with adjustable characteristics mainly concerning the number ofpulses (2 to 6 pulses) and the individual pulse peak power (0.2Ñ2.3 MW).
This paper shows experimental and theoretical results obtained with an oscillator-amplifier XeCl laser system of short duration (3 ns) and high energy. This laser system is based on a four pass amplification scheme with off-axis incidence to the active medium to minimize the formation of the Amplified Spontaneous Emission in the amplifier. In this configuration, pulses of approximately 10.2 mJ energy and of 3.8 ns duration have been obtained with a high contrast. These results are discussed and compared to numerical ones issued from a numerical code describing the amplification of the oscillator beam in the active medium.
Many kinetic and spectroscopic studies were performed on alkali rare gas ionic excimer. The main results obtained during these investigations are presented. We observed fluorescence spectra from diatomic and triatomic molecules. Vacuum ultraviolet fluorescence emissions from alkali rare gas ionic excimer molecules were studied in detail by low- energy electron beam excitation. Measurements were performed as a function of gas composition, gas pressure and deposited energy in order to investigate the kinetic mechanisms of these molecules. The rate constants of the formation and competitive reactions were determined from the observed fluorescence signal decay.
The application of excimer laser ablation process to the decontamination of radioactive surfaces is discussed. This technology is very attractive because it allows to efficiently remove the contaminated particles without secondary waste production. To demonstrate the capability of such technology to efficiently decontaminate large area, we studied and developed a prototype which include a XeCl laser, an optical fiber delivery system and an ablated particles collection cell. The main physical processes taking place during UV laser ablation will be explained. The influence of laser wavelength, pulse duration and absorption coefficient of material will be discussed. Special studies have been performed to understand the processes which limit the transmission of high average power excimer laser through optical fiber, and to determine the laser conditions to optimize the value of this transmission. An in-situ spectroscopic analysis of laser ablation plasma allows the real time control of the decontamination. The results obtained for painting or metallic oxides removal from stainless steel surfaces will be presented.
Energetic nanosecond UV sources could be advantageously used in laser material processing, biomedicine and to create laser- produced plasmas emitting soft X-ray radiation. SOPRA, in collaboration with IRPHE, is then developing an oscillator- regenerative amplifier XeCl laser system of short duration (1 - 3 ns), high energy and moderate divergence. Insertion in the amplification loop of the seed pulse and final extraction of the amplified laser pulse are realized by controlling the evolution of its polarization state by means of a HT driven Pockels cell and a half-wave plate. The experimental results are discussed and compared to numerical ones issued from a code describing the amplification of the seed pulse in the active medium. Finally, it is shown that the maximum output peak power is fairly low, PL approximately 1.4 MW (EL approximately 4.8 mJ, (tau) FWHM approximately equals 3.4 ns), due to important energetic loss as the highly divergent amplified beam is truncated by low-diameter aperture.
We introduce a numerical investigation of a HF photochemical laser pumped by planar multi-channel sliding discharge to study the possibility of advanced laser characteristic achievement using such pumping source. The model considers transport of VUV pump radiation through the nonlinear absorptive active medium containing NF3/H2/N2Ar gas mixture coupled with chemical and lasing kinetics describing the temporal and spatial evolution of particle species and intracavity lasing photons. The relative importance of various kinetic processes is evaluated and the 3.2 J/liter laser specific energy is calculated.
The excimer laser nitriding process reported is developed to enhance mechanical properties of aluminum alloys. An excimer laser beam is focused onto the alloy surface in a cell containing 1 bar nitrogen gas. A vapor plasma is expanding from the surface and shock wave dissociates and ionizes nitrogen. Then vapor and gas species stay several hundreds of microsecond(s) in contact with the surface and nitrogen diffuses in depth. Thus it is necessary to work with a sufficient laser fluence to create the plasma, but this fluence must be limited to prevent from a too large laser-induced surface roughness. The nitrogen concentration profiles are determined from RBS and SEM coupled to EDX probe analysis. The roughness and surface state are studied to define the best irradiation conditions corresponding to a smooth and homogeneous surface.
Surface removal technologies are being challenged from environmental and economic perspectives. This paper is concerned with laser ablation applied to large surface cleaning with an automatized excimer laser unit. The study focused on metallic surfaces that are oxidized and are representative of contaminated surfaces with radionuclides in a context of nuclear power plant maintenance. The whole system is described: laser, beam deliver, particle collection cell, real time control of cleaning processes. Results concerning surface laser interaction and substrate modifications are presented.
Ultraviolet excimer lasers are attractive candidates to generate efficiently high brightness soft X-ray sources. Preliminary results on the development of an oscillator- amplifier excimer laser system based on the regenerative amplifier technique are presented. These experiments have been performed in collaboration with the laser company SOPRA in the frame of the EUREKA-EXULT (EU-1182) program.
A numerical code has been developed to simulate the characteristics of HF chemical laser based on non-chain reaction pumped by a planar sliding discharge radiation. The model considers transport of VUV pump radiation through the nonlinear absorptive active medium containing NF3/H2/N2/Ar gas mixture coupled with chemical and lasing kinetics describing the temporal and spatial evolution of particle species concentration and intracavity lasing photons density. The relative importance of various kinetic processes is evaluated and a 3.2 J/l laser output specific energy is calculated along the laser axis.
Vacuum ultraviolet fluorescence emissions of alkali rare gas triatomic ionic excimers have been observed. These molecules have been produced by electron beam excitation of rare gas alkali mixtures at high pressure and high temperature. Spectroscopic and kinetic studies have been performed on Kr2+Cs ions which exhibit a spectrum centered at 159nm. Binding energy of the lowest excited state has been estimated. Simple kinetic considerations allowed us to propose two formation processes of these ions and to estimate their rate constant.
The uniformity and stability of discharge process in a high pulse repetition frequency long pulse XeCl laser are investigated for three different copper electrode roughnesses in single shot regime and versus PRF. The discharge quality evolution is experimentally analyzed from discharge photographs obtained with CCD video camera and pressure perturbation measurements achieved with a piezoelectric pressure probe placed very close to the discharge volume.
Transmission of XeCl excimer laser pulses through commercial silica optical fibers with high OH content have been investigated. The Ultraviolet irradiation of these optical fibers includes color center generation and two photon absorption in the fiber core. These absorbing centers disappear at room temperature. A spectroscopic study of fiber core fluorescence permitted to clearly identify the Non Bridging Oxygen Hole Centers as main type of defects created. The influence of laser parameters on transmission evolution of the optical fiber observed during irradiation are discussed. The use of a bundle of fibers to transmit high average power excimer laser is presented. The results obtained in these experiments are promising for the use of optical fibers in a wide range of excimer laser industrial applications.
Alkali rare gas triatomic ionic excimers have been observed for the first time. These molecules have been produced by electron beam excitation of rare gas alkali mixtures at high pressure and high temperature. Emission spectra centered at approximately 159 nm have been observed and attributed to Kr2+Cs ions. Lifetimes and binding energies of the lowest excited states have been estimated. Simple kinetic considerations allowed us to propose two formation processes of these ions and to estimate their rate constant.
The uniformity and stability of discharge process in a high pulse repetition frequency (PRF) long pulse XeCl laser are investigated for three different copper electrode roughnesses versus PRF (f less than or equal to 500 Hz; 10 shots). The discharge quality evolution is experimentally analyzed from discharge photographs obtained with a CCD video camera and pressure perturbation measurements achieved with a piezoelectric pressure probe placed very close to the discharge volume.
The uniformity and stability of discharge process in a high pulse repetition frequency (PRF) long pulse XeCl laser are investigated for three different electrode materials (aluminum, copper, brass) and different roughnesses of the copper electrode versus PRF (f less than or equal to 700 Hz) for burst durations of 10 shots. The discharge quality evolution is experimentally analyzed from discharge photographs obtained with a CCD video camera and pressure perturbation measurements achieved with a piezoelectric pressure probe placed very close to the discharge volume.
Uniformity and stability of discharge process in a high Pulse Repetition Frequency (PRF) long pulse XeCl laser are investigated for three different cathode materials (aluminium, copper, brass) versus PRF (f <EQ 700 Hz) and burst duration (1 - 100 shots). The discharge quality evolution is experimentally studied with a fast gated CCD video camera providing 200 - 400 ns time-integrated discharge photographs. This discussion also benefits from a theorical approach of the macroscopic properties of the different cathode materials and from the development of a simple code calculating the shot to shot electrode temperature increase due to the successive input energy releases.
The feasibility of coupling in and transmitting high average power UV radiation down fused silica fiber without damage has been demonstrated in burst mode. The approach we have followed to transmit high average XeCl laser powers is to use modest laser energies at very high repetition rates, because the induced attenuation coefficient at high repetition rate is likely to be less than that which would occur using a high fluence modest repetition rate approach. We have also chosen to utilize a long optical pulse duration XeCl laser made possible using a magnetic-spiker excitation circuit. For a given laser fluence coupled into the fiber, the low peak power long pulses reduce the probability of intensity dependent effects such as catastrophic surface damage and color center formation. The influence of pulse duration, repetition rate and laser beam quality on fiber optic transmission will be discussed. An output average power of 75 W (in a burst mode) of XeCl laser radiation has been transmitted through a single step-index fused silica fiber using a high repetition rate (820 Hz), long optical pulse (180 ns (FWHM)) magnetic-spiker excited XeCl laser.
A parametric study of long pulse XeCl laser is undertaken at IMFM in the frame of EUREKA EU 205 program, with the aim to optimize such lasers in terms of efficiency and laser average power at high PRF. These developments have important issues in applications. In particular there is a need for short wavelength, high energy lasers with long pulse duration, in order to overcome the limitations of present laser sources for transmission through optical fiber, namely fiber input surface degradation and two photons absorption which are optical power dependent. An X-ray preionized spiker-sustainer XeCl excimer laser operating at high repetition frequency (1000 Hz) and 220 W of average power with 2.4% efficiency is demonstrated with use of LUX Test-Bed. Pulse energy and pulse duration (160 ns) are virtually independent of pulse rate frequency. Comparison with CLC circuit XeCl laser excitation for the same operating conditions shows superior properties of spiker-sustainer excitation for high frequency operation due to higher efficiency and discharge homogeneity and stability. As an example with CLC circuit excitation laser average power saturate at 400 Hz without acoustic dampers and at 800 Hz with use of dampers while with spiker-sustainer circuit no saturation is observed up to 1200 Hz (limited by available electrical power) without use of acoustic dampers. Experimental results on laser behavior at high PRF are presented as well as a study of acoustics perturbation induced by the discharge inside LUX by means of fast pressure piezoelectric probes. Pressure probes signals show a reduction by a factor 2.5 of pressure waves amplitude in the immediate vicinity of laser cavity with spiker-sustainer circuit as compared to CLC circuit. This strong decrease is attributed mostly to the higher discharge stability and also to the higher efficiency obtained with spiker-sustainer circuit.
In this paper, we are reporting for the first time on a spiker-sustainer XeCl laser operating at a PRF of up to 1 kHz. The laser is x-ray pre-ionized in the interest of pre-ionization homogeneity and in order to avoid contamination of the laser gas. A conventional flow loop was employed, having a maximum flow speed of 50 m/s at 3 bar, which translates into a clearing ratio of 2.5 at a PRF of 1 kHz. A pyroelectric energymeter (GenTec ED500) was used to measure single-shot energies. The pulse energy in repetitive mode and the pulse duration were observed with a calibrated vacuum photodiode. The spatial beam profile was recorded on photosensitive Dylux paper. Among the different spiker modes tested, a modification of the overshoot mode gave the best results in terms of efficiency, output energy, and overall laser stability.
Acoustic phenomena may play a leading role in high average power excimer laser as soon as a high pulse repetition rate is achieved. In this paper we demonstrate both experimentally and theoretically that acoustic wave generation and evolution are strongly dependent on electric arcs appearing at the end of the discharge. These acoustic waves induce a strong decrease of laser power throughout an amplification phenomenon of pressure fluctuations at high PRF. Acoustic dampers allow us to reduce this phenomenon and to increase the laser output power up to 50%.
Improvement in efficiency and specific output energy on an XeCl long pulse laser ((lambda) equals 308 nm) and the first achievement of long pulse (150 ns FWHM) laser emission from KrCl (B - > X) at (lambda) equals 222 nm are reported. The system, which includes x- ray preionization and double discharge (pulser/sustainer) excitation, allows potentially high laser efficiency from a small volume active medium with relatively low pressure Ne/Xe/HCl, Ne/Xe/BCl3, Ne/Kr/HCl and Ne/Kr/BCl3 working mixtures.
A theoretical analysis is made to describe the influence of an active disturbing medium on the far-field diffraction pattern of an excimer laser beam. Results are in good agreement with experiences. The gas density perturbations induce amplitude and phase aberrations which are responsible for the degradation of the beam characteristics in the far-field.
Thin films of Y1Ba2Cu3O7-x were deposited via pulsed laser ablation onto MgO and YSZ (Yttria-Stabilized Zirconia) substrates. The use of an IR Nd:YAG laser leads to nonstoichiometric deposition. The best quality superconducting films were deposited by means of UV excimer laser ablation ((lambda) equals 308 nm). These films were strongly orientated with c-axis perpendicular to (100) substrate. The film quality was found to be strongly dependent on substrate temperature, oxygen pressure, sample cooling rate and laser fluence. The deposition process was characterized by the time-resolved spectroscopic measurements of the emission from YO molecules.
An experimental parametric study of a small volume x-ray preionized XeCl laser which uses the double discharge (spiker-sustainer) principle and a new fast ferrite magnetic switch is presented. This high-efficiency discharge excitation system, with a Ne/Xe/HCI mixture at relatively low pressure (P equals 2.5 atm.), in a 50 cm3 active volume (25(DOT)2(DOT)1 cm3), has made possible an efficiency of 3.2% in energy and 4% in power at maximum with up to 140 mJ of extracted optical energy in a 130 ns (FWHM) laser pulse in switch mode. The authors discuss laser characteristics dependence with magnetic switch and electrical circuit parameters, for switch mode. Future studies of the present advanced excitation system for conditions of very high PRF, in the frame of Eureka EU205 Eurolaser program, are presented. The experimental part of these planned studies will be made with LUX very high PRF high average power IMFM test-bed
A complete model of a long-pulse x-ray preionized self-sustained discharge XeCl excimer laser has been established for the case of excitation by an advanced electrical circuit associating a double discharge (spiker/sustainer) and a fast low-loss ferrite magnetic switch with pulsed reset. This model allows simulation of the potential working conditions of the IMFM high average power, very high repetition rate LUX test-bed. The model, which considers Ne as buffer gas and HCl as halogen donor, includes a rate equation for species with the most recent available rate constant values, circuit equations with time-dependent ferrite inductance and plasma impedance and rate equation for laser emission taking into account absorbtions. Modeling takes into account time delay between spiker and sustainer, low value of sustainer field and dynamics of magnetic switch. The model has been validated with a long- pulse x-ray preionized XeCl laser, with double discharge and magnetic switching, developed at IMFM, which has already obtained over 3% efficiency and 140 mJ extracted energy in 150 ns (FWHM) from a 50 cm3 active volume at 2.5 atm. pressure. Numerical results are in good agreement (within 30%) with IMFM experimental results. A parametric study of the XeCl laser with double discharge and fast magnetic switch is presented as well as a comparison with both experiments and numerical results of excitation by a C-L-C classical circuit for the same geometric and gas conditions and the same input energy.
A complete model of the long pulse XeCI excimer laser excited by a double discharge with fast magnetic switch has been established for an Ne/Xe/HCI active medium. This model simulate one of the potential working conditions of the IMFM high average power LUX test-bed. Model includes rate equations for species with most recent availiable rate constant values, circuit equations with time dependant ferite switch inductance and plasma impedance and rate equation for laser emission taking into account absorptions. The model allows to simulate very long laser pulses (150-200 ns) and numerical results are in good agreement (within 30 %) with experimental results obtained at IMFM.
Acoustic and aerodynamic phenomena may play a leading role in high average power excimer laser as soon as a high pulse repetition rate is envisioned. This general lecture summarizes the studies achieved at IMFM on this topic.
To increase the pulse repetition frequency, the average power, and the beam quality of excimer
laser systems, damping of the strong acoustic waves induced by the active medium excitation must
be solve. In order to achieve this goal different electrodes and acoustic damping configuration have
been studied.
Excitation of active medium (energy deposition : 50 to 150 J/l) at high repetition rate
(up to 1 000 Hz) in a subsonic loop (flow velocity : up to 65 m/s) is achieved by means of a classical
discharge, through transfers capacitors. The discharge is preionized by X-Ray generated by a wire ion
plasma gun.
Previous studies done at I.M.F.M. have shown that the density perturbations, induced by
successive excitations at high repetition rate (up to 1000 Hz), can involve output energy decrease.
Here, we will present and discuss the density or pressure perturbation maximum level which
don't involve this laser energy decrease; acoustic and thermal effects have been notably took account.
We will study the possibilities of fast pressure perturbations damping.
High efficiency X-ray Preioized discharge XeCl laser e,citation has been achieved with a
Ne/Xe/HCI mixture in a 50 cm" active volume (25*21 cm'), by combining double discharge
technique (spiker/sustainer) with a new fast ferrite magnetic switch. A fast high voltage spiker pulse of
low energy is applied across laser electrodes to initiate an uniform discharge. Peaking capacitors are
set in a very low inductance configuration between electrodes. Main discharge is energized by a 200ns
electrical time pulse charged double sided solid state PFL of much lower voltage which is
automatically applied to electrodes through a low inductance path after magnetic switch saturation by
the spiker.The magnetic switch is made of several coaxial structures in parallel, each of them
comprising many high frequency Ni-Zn ferrite tores set in serie. This laser has a very high pulse rate
frequency capability (> 1 KHz). An efficiency over 3% in energy and 4% in power at the maximum, with
110 mJ extracted optical energy in a 140 ns (FWHM) laser pulse length, has been demonstrated with
this not optimized device.A parametric study of this laser is presented. At the end, planned further
studies of the present advanced excitation system for conditions of very high PRF, in the frame of
Eureka EU205 Eurolaser program, are presented. The experimental part of these planned studies
would be made with LUX very high PRF high average power IMFM test-bed.
To obtain a high average laser output power and a good quality laser beam in high repetition
rate excimer lasers, it is necessary to swept the heated gas out of the laser cavity between two
electrical excitations and to damp density fluctuations induced by acoustic and shock waves. In this
aim, a numerical study of an unsteady two-dimensional flow inside the laser head has been
undertaken at I.M.F.M. This study is extended to the case when mufflers are added in the
surroundings of discharge zone. The work is achieved by means of a numerical model based on a
finite difference scheme with a flux corrected transport algorithm (Shasta. F.C.T. method). This method
allows to simulate the propagation of longitudinal (along the flow) and transversal (between the
electrodes) shock waves induced by the active medium excitation, and the effects of acoustic
dampers on the density fluctuations. Transversal acoustic waves are induced by the non-uniformity of
energy deposited between the electrodes. The model uses two dimensional Euler equations in the
laser flow channel and one dimensional Euler equations in the acoustic damper (grid and porous
material). Several comparisons between experimental and numerical results have been performed to
establish the model validity. The influence of the acoustic dampers on the transversal wave decay
process in a laser cavity is presented.
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